The goal of this research is to examine the patterns of substance use over time among an existing cohort of HIV positive and negative men who have sex with men (MSM) participating in the Multicenter AIDS Cohort Study (MACS). An important health issue that has received little research attention is how the patterns of substance use among MSM are carried from early age into later life and whether distinct patterns of substance use are associated with decreased functioning, increased health and social problems as MSM age. While research among heterosexual men has found a fall-off or decrease in drug use with increased age, existing research among MSM has not observed a substantial decline in drug use across the life course. This proposal seeks funding to conduct a mixed method study that includes 1) an innovative approach to secondary quantitative data analysis of existing MACS data and 2) qualitative in-depth interviews with select MACS participants. The analysis will compare trajectories of declining substance use with increasing or consistently high levels of use. These pattern comparisons will allow for the identification of resiliency characteristics associated with decreased substance use and related health and social problems. Results will be used as the basis of a future R21 grant application to develop and evaluate a model intervention to prevent substance abuse and related health and social problems among both HIV positive and negative MSM. Quantitative findings regarding the factors that contributed to decreased substance use over time and qualitative data regarding how the participants manage their substance use over time have direct implications for development of a strengths-based intervention. The analysis will also specifically seek to develop hypotheses from the qualitative and quantitative data that can be tested with other aging populations of substance users. Little is known regarding how substance use patterns change or stay stable as MSM age and the factors influencing patterns of change or stability in substance use across the life course. The results of this research will allow for the identification of resiliency characteristics associated with decreased substance use and related health and social problems and will be used as the basis for a future grant application to develop and evaluate a model intervention to prevent substance abuse and related health and social problems among both older HIV positive and negative MSM.